Jurassic semiaquatic mammal relative Megacauda found in China, with throat anatomy preserved

Mixed · 2Researchers have described Megacauda sungei, a new genus of mammaliform (a mammal relative) found in China, which they say is the earliest known semiaquatic mammaliform. 1 2 Mixed · 2The fossil is dated to roughly 163 to 168 million years ago, in the Jurassic, when dinosaurs dominated the planet. 2 1 Mixed · 2ABC News reports that a study in Nature places Megacauda in the extinct Docodonta branch, early cousins of true mammals. The name refers to its broad tail and to palaeontologist Sun Ge. 1 2

Mixed · 2The fossil came from Inner Mongolia. New Scientist says local farmers found it in the Daohugou area. ABC says it was found in 2015 in the Haifanggou Formation, a rock layer that senior author Zhe-Xi Luo of the University of Chicago called "teeming with salamanders". 2 1 Mixed · 2The animal weighed about 1 to 2 kilograms (New Scientist estimates 1 kilogram), making it the largest known mammaliform of its period. ABC compares its size to a modern platypus. 1 2 Mixed · 2Luo described it as a mix: the back half resembles a platypus, while the skull and teeth are comparable to a river otter's. Suzanne Hand, an emeritus professor at the University of New South Wales who was not involved, pointed to platypus-like foot, ankle and pelvis shapes, webbed feet, a flattened tail and thick fur. Luo noted differences too, including strong canine and sectorial teeth for eating meat in water. 2 1

Mixed · 2The fossil preserves the pelvis in 3D and the throat (hyoid) bones, allowing the first reconstruction of a mammaliform's entire throat anatomy. The researchers say it was built for milk feeding in infancy and swallowing food in adulthood, as in modern mammals. 2 1 Centre · 1New Scientist presents this as evidence that suckling arose before today's mammals. Oliver Griffith of Macquarie University, who is quoted but not described as an author, said traits like sucking, which is needed to drink a mother's milk, predate the origin of living mammals. 2 Mixed · 2Tiny limb fragments resembling salamander bones were found in the stomach area and may be its last meal. Luo said the carnivorous teeth suggest it could eat small fish and salamanders. 2 1

Left · 1Luo said the find suggests the ability to swim arose early in mammal evolution. Hand listed possible reasons semiaquatic life evolved repeatedly, including access to rich food and less competition, and said study of limb-bone microstructure could show how much time it spent in water. 1 Left · 1ABC says Megacauda replaces Castorocauda, a beaver-like creature from 164 to 159 million years ago, as the earliest known semiaquatic mammaliform. It adds that the earliest known semiaquatic true mammal, Dongoconodon platycauda, is about 120 million years old, and that the oldest platypus fossil is only about 3.8 million years old. 1